term% cat index.txt DD(1) General Commands Manual DD(1)
NAME
dd - convert and copy a file
SYNOPSIS
dd [option=value] ...
DESCRIPTION
Dd copies the specified input file to the specified output with possi‐
ble conversions. The standard input and output are used by default.
The input and output block size may be specified to take advantage of
raw physical I/O.
option values
if=file input file name; standard input is default
of=file output file name; standard output is default
ibs=n input block size n bytes (default 512)
obs=n output block size (default 512)
bs=n set both input and output block size, superseding ibs
and obs; also, if no conversion is specified, preserve
the input block size instead of packing short blocks
into the output buffer. This is particularly efficient
since no in-core copy need be done.
cbs=n conversion buffer size
skip=n skip n input records before starting copy
files=n copy and concatenate n input files before terminating
(makes sense only where input is a magtape or similar
device).
seek=n seek n records from beginning of output file before
copying
count=n copy only n input records
conv=ascii convert EBCDIC to ASCII
ebcdic convert ASCII to EBCDIC
ibm slightly different map of ASCII to EBCDIC
block convert variable length ASCII records to fixed length
unblock convert fixed length ASCII records to variable length
lcase map alphabetics to lower case
ucase map alphabetics to upper case
swab swap every pair of bytes
noerror do not stop processing on an error
sync pad every input record to ibs
... , ... several comma-separated conversions
Where sizes are specified, a number of bytes is expected. A number may
end with k, b, or w to specify multiplication by 1024, 512, or 2 re‐
spectively; a pair of numbers may be separated by x to indicate a prod‐
uct.
Cbs is used only if ascii, unblock, ebcdic, ibm, or block conversion is
specified. In the first two cases, cbs characters are copied into the
conversion buffer, any specified character mapping is done, trailing
blanks are trimmed and new-line is added before sending the line to the
output. In the latter three cases, characters are read into the con‐
version buffer and blanks are added to make up an output record of size
cbs. If cbs is unspecified or zero, the ascii, ebcdic, and ibm options
convert the character set without changing the block structure of the
input file; the unblock and block options become a simple file copy.
After completion, dd reports the number of whole and partial input and
output blocks.
EXAMPLE
dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase
Read an EBCDIC tape blocked ten 80-byte EBCDIC card images per
record into an ASCII file. Note the use of raw magtape to han‐
dle arbitrary record sizes.
SEE ALSO
cp(1), tar(1), cpio(1)
DIAGNOSTICS
f+p records in(out) numbers of full and partial records read(written)
BUGS
The ASCII/EBCDIC conversion tables are taken from the 256 character
standard in the CACM Nov, 1968. The ibm conversion, while less blessed
as a standard, corresponds better to certain IBM print train conven‐
tions. There is no universal solution.
DD(1)